The objective of this proposal is to investigate the effects of intrauterine malnutrition on neonatal lymphocyte function and the correlation between lymphocyte function and risk of neonatal infection. Specifically, we propose to study lymphocyte mitogen-induced proliferation and class-specific immunoglobulin biosynthesis following in utero malnutrition and the correlation between these responses and the development of neonatal infection. Lymphocytes will be studied 1) from the cord blood of 28-44 week gestational aged infants following adequate and inadequate in utero nutriton, and 2) from serial heel stick blood specimens from birth to 4 months of age in full-term newborns exposed in utero to either adequate or inadequate nutrition. The clinical status of neonates in both phases of study will be monitored noting all episodes of suspected or proven infection and these data will be correlated with the measured lymphocyte responses. Finally, the immunoenhancing effect of bovine thymosin on cord blood lymphocyte mitogen-induced responses will be measured. These three phases of investigation will outline the ontogeny of mitogen-induced fetal lymphocyte proliferation and immunoglobulin biosynthesis through the third trimester of gestation and will correlate these responses with both the neonates in utero nutritional status and risk of developing infection. Simultaneously, it will allow one to determine the normal changes in mitogen-induced responsiveness over the first 4 months of life, any alteration in these changes characteristic of SGA infants, and the correlation between these changes in lymphocyte responsiveness and development of infection. Finally, the investigation of thymosin as an immunoenhancer may offer supportive data for subsequent therapeutic intervention in malnourished neonates, perhaps resulting in reduced morbidity and mortality.